Relationship between microsatellite instability, response and survival in palliative patients with colorectal cancer undergoing first-line chemotherapy

Background and Aims: The aim of this work was to investigate the relationship between microsatellite instability (MSI), treatment response and survival in palliative patients with colorectal cancer (CRC) undergoing first-line treatment with weekly, 24-hour infusion (24-h inf.) of high-dose 5-fluorouracil (5-FU) and folinic acid (FA). Patients and Methods: Tumour material from the colorectal primary carcinomas was analysed for 43 patients. MSI analysis was carried out and immunohistochemistry was performed with hMLH1 and hMSH2. Results: Tumours of 7 patients (16%) were highly instable (MSI-H). These patients had a better response rate (72% vs. 41%, p=0.072) and a significantly better median survival (33 months, [95% CI 20-46] vs. 19 months, [95% CI 10-28]: p = 0.021) than microsatellite stable (MSS) patients (n = 36). Furthermore, MSI status was shown to be an independent predictive marker for survival (p = 0.037). Conclusion: These data provide further support for the hypothesis that MSI-H CRC might have a better response and survival than (MSS) CRC in palliative first-line treatment.